Adjusting Thread Tension

Tension is like a tug-of-war between the bobbin thread and the top thread—ideally, both should be of equal strength. If you could cut through a seam vertically, the bobbin and top threads would be interlocking in the middle (see picture A).

If the top thread is too tight, the bobbin thread will be visible on the upper side; if the top thread is too loose, the top thread will show on the underside (see picture B).

It’s easier to adjust top tension than bobbin tension simply because the upper adjustment has numbers; the bobbin tension is adjusted with a screw and no numbering system. When adjusting either, remember that “righter is tighter, and le er is looser.”

Some machines adjust tension automatically based on fabric and thread information you provide; others require manual adjustment when you change thread types, sew on heavy fabrics, or use a decorative stitch.

Poor tension will affect not only the look of your stitched seam but also the durability—loose tension can cause the seam to pull out; tight tension can cause it to pucker. So, make adjustments in small increments if needed until stitching looks balanced.

Always test-stitch and ﬁne-tune when you think there might be a tension adjustment needed. Keep a notebook of samples with tension settings written on the swatches.